Merohedral disorder and impurity impacts on superconductivity of\n fullerenes

Abstract

Local quasiparticle states around impurities provide essential insight into\nthe mechanism of unconventional superconductivity, especially when the\ncandidate materials are proximate to an antiferromagnetic Mott-insulating\nphase. While such states have been reported in atom-based cuprates and\niron-based compounds, they are unexplored in organic superconductors which\nfeature tunable molecular orientation. Here we employ scanning tunneling\nmicroscopy and spectroscopy to reveal multiple forms of robustness of an exotic\n$s$-wave superconductivity in epitaxial Rb$_3$C$_{60}$ films against merohedral\ndisorder, non-magnetic single impurities and step edges at the atomic scale.\nAlso observed have been Yu-Shiba-Rusinov (YSR) states induced by deliberately\nincurred Fe adatoms that act as magnetic scatters. The bound states display\nabrupt spatial decay and vary in energy with the Fe adatom registry. Our\nresults and the universal optimal superconductivity at half-filling point\ntowards local electron pairing in which the multiorbital electronic\ncorrelations and intramolecular phonons together drive the high-temperature\nsuperconductivity of doped fullerenes.\n